The present invention relates to an improvement of a cooling system for rotary electric machines with salient magnetic poles such as water-wheel generators. More particularly, the invention relates to an improvement of an air cooling system for rotary electric machines with shield plates each bridging the tips of adjacent magnetic poles in which the cooling air flowing in a space formed between the adjacent magnetic poles is discharged through an air-discharge window of the shield plate and air discharge ducts formed radially in the stator core to the outside of the stator frame.
There have been many proposals of cooling systems for rotary electric machines of medium size and some of them have been brought into practice. In the field of the rotary electric machines, a recent trend is to increase the capacity of a single machine, which necessarily requires a larger amount of cooling air flowing through the machine. This, however, gives rise to the windage loss problem in the cooling air flow. Some solutions of the problem are disclosed in, for example, U.S. Pat. No. 3,514,647 issued May 26, 1970 to Norman J. Lipstein, entitled "Cooling Arrangement For Dynamoelectric Machines", U.S. Pat. No. 3,106,654 issued Oct. 8, 1963 to Adolph J. Wesolowski, entitled "Salient Pole For Synchronous Machines" and Japanese utility model application Ser. No. 2690/75, laid-open as laid-open No. 82902/76 and entitled "Salient Pole Rotor". In those solutions, shield plates are provided to bridge the tips of every adjacent magnetic poles so that the rotor gives a substantially cylindrical configuration, thereby to lower the windage loss on the outer surface of the rotor. The construction of the rotary electric machine thus designed and the flows of the cooling air within the machine will be described referring to FIGS. 1 and 2. In the figures, reference numeral 1 designates a shaft; 2 a yoke mounted to the shaft 1; 4 salient magnetic poles; 5 a field coil; 6 a shield plate closing a space between the adjacent salient magnetic poles to lower the windage loss on the outer surface of the rotor.
In the stator, a stator winding 7 is wound around a stator core 8, fitting in the slots of the core 8. Reference numeral 9 is a duct permitting cooling air flow therethrough to cool the core 8 and numeral 10 designates a stator frame including a plurality of partition plates 10a. Numerals 11 and 12 represent first air flow guides for introducing cooling air into the rotary electric machine. Numerals 13 and 14 represent second air flow guides for providing an air path for the cooling air which is effective, in cooperation with the fan action by the salient poles, to decrease the amount of cooling air flowing back toward the spaces between the adjacent magnetic poles. Numerals 15 and 16 indicate first blowers for forcibly feeding cooling air through the spaces between the magnetic poles to cool the field winding 5 and the iron core. Box-shaped air collectors 17 and 19 well illustrated in FIG. 2 collect air flowing into and from the rear side of the stator core 8. A cooler 18 is mounted on the air collector 17. A second blower 20 for cooling the stator is similarly mounted on the air collector 19. A foundation of concrete designated by reference numeral 21 supports the rotary electric machine.
The cooling air within the rotary electric machine thus constructed flows as follows. For cooling the field winding 5, both the first blowers 15 and 16 feed cooling air into the space between the adjacent magnetic poles 4. The cooling air, then, flows through an window 50 opened at the axially central part of the shield plate 6 bridging the space between the adjacent magnetic poles 4 and a part of air-discharge ducts 9a located at the axial center portion of the stator core and having substantially the same axial size as the window 50 into the cooler 18. For cooling the stator, the second blower 20 blows cooling air into the rear side of the stator. The cooling air passes through inflow sections 22 and the ducts 9 to flow out through an air gap g. The cooling air guided into the gap g is bent to flow into air discharge ducts 9a. The cooling air, then, passes through the outflow section 23 towards the cooler 18.
This type rotary electric machine thus constructed and cooled suffers from the following shortcomings which will be described with reference to FIG. 3. A cooling air flow a discharged through a portion not covered by the shield plate 6, i.e. the window 50, toward the air gap g interferes with an air flow in the stator side, resulting in reducing the amounts of air flows of the stator and rotor sides. That is, the fan action of the salient magnetic poles causes the air flow a to blow at a high pressure into the air gap g and the stator side. In this case, the air flow a flows in a direction the same as the flow b in the outflow section 23 but opposite to the flow c in the inflow section 22. Accordingly, the amount of cooling air flow d from the rear side of the stator to the air gap g is considerably reduced. Further, the cooling air flows through the ducts which are located near the boundary between the outflow section and the inflow section decreases greatly because it is against the cooling air flow a from the rotor. The failure of cooling air flow may cause a high temperature rise at the area resulting in the coil being damaged due to local heating.
The air flow a from the rotor side interferes with the air flow in the stator side thereby increasing the air-flow resistance so that the amount of air flow in the rotor side also reduces greatly.